A light irradiation substrate is provided which can cope with cases of emergency and which is capable of optimum irradiation with therapeutic light regardless of the shape or size of affected parts while keeping a lid on cost. The center-to-center distance between two adjacent LED chips (13) facing each other across the boundary between two unit substrates (7) adjacent to each other in an X direction or (a Y direction) and belonging to the respective unit substrates (7) is twice or less as long as the center-to-center distance between two LED chips (13) adjacent to each other in the X direction (or the Y direction) within each of the unit substrates (7). Each of the unit substrates (7) includes a connection section (10) that provides external connection of wires (12). The connection section (10) is provided on a back surface of a flexible substrate (6).
